am401826g_si_004.mpg (1.89 MB)
Simple Strategy for Producing Superhydrophobic Nanocomposite Coatings In Situ on a Building Substrate
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posted on 2013-08-14, 00:00 authored by Dario
S. Facio, Maria J. MosqueraNumerous
superhydrophobic materials have been developed in recent years by
using a combination of two strategies: reducing the surface free energy
and roughening the surface. Most of these procedures have the serious
drawback of involving tedious multistage processes, which prevent
their large-scale application, such as on the external stone and similar
material surfaces of buildings exposed to the weather. This paper
describes an innovative synthesis route for producing superhydrophobic
surface coatings. The coating can even be produced, outdoors, on the
building by a low-cost process. We demonstrate that the addition of
silica nanoparticles to a mixture of organic and inorganic silica
oligomers in the presence of a surfactant produces a coating of closely
packed particles. The effect of this is to trap air beneath the water
droplets, thus significantly minimizing the contact area between droplet
and surface. The organic component reduces the surface free energy
of the material, resulting in a high static contact angle. This has
the effect of repelling water because the water droplets that form
simply roll rapidly down the coated surface. The surfactant plays
a valuable role, acting as a sol–gel transition catalyst and,
by coarsening the pore structure of the gel network, prevents the
coating material from cracking.